Registers a function that is called without arguments at program
    termination.

    Format

      #include  <stdlib.h>

      int atexit  (void (*func) (void));

1 - Argument

 func

    A pointer to the function to be registered.

2 - Return Values

    0                  Indicates that the registration has succeeded.
    nonzero            Indicates failure.

3 - Restriction

    The longjmp function cannot be executed from within the handler,
    because the destination address of the longjmp no longer exists.

4 - Example

        #include <stdlib.h>
        #include <stdio.h>

        static void hw(void);

        main()
        {
            atexit(hw);
        }

        static void hw()
        {
                puts("Hello, world\n");
        }

      Running this example produces the following output:

        Hello, world